Combined thermal-magnetic trip means for circuit breakers

ABSTRACT

A CIRCUIT BREAKER FOR PROTECTION AT RELATIVELY LOW CURRENT VALUES, AND HAVING BOTH THERMAL AND MAGNETIC TRIP MEANS, IS PROVIDED WITH A DIRECTLY HEATED THERMAL ELEMENT WHICH UPON DEFLECTION THEREOF REDUCES THE WIDTH OF THE   MAGNETIC SYSTEM AIR GAP TO A POINT AT WHICH THE MAGNETIC SYSTEM IS EFFECTIVE TO UNLATCH THE CIRCUIT BREAKER CONTACT OPERATING MECHANISM.

Jan. 12, 1971 F. MYERS I 3,555,463

. COMBINED THERMAL-MAGNETIC TRIP MEANS RoR CIRCUIT BREAKERS Filed sept. 2, 1969 2 sheets-Sheet 1 l Jan. 12, 1971 F. E. MYERSl y 3,555,468l

COMBINED THERMAL-MAGNETIC TRIP MEANS FOR CIRCUIT BREAKERS Filed Sept.- 2, 1969 2 Sheets-Sheet 2 United States Patent 3,555,468 COMBINED THERMAL-MAGNETIC TRIP MEANS FOR CIRCUIT BREAKERS Felix E. Myers, Cherry Hill, NJ., assignor to I-T-E Imperial Corporation, a corporation of Delaware Filed Sept. 2, 1969, Ser. No. 854,706 Int. Cl. H01h 75/10 U.S. Cl. 335-36 10 Claims ABSTRACT OF THE DISCLOSURE A circuit breaker Vfor protection at relatively low current values, and having both thermal and magnetic trip means, is provided with a directly heated thermal element which upon deilection thereof reduces -the width of the magnetic system air gap to a point at which the magnetic system is eifective to unlatch the circuit breaker contact operating mechanism.

This invention relates to circuit breakers in general, and more particularly relates to circuit breakers for protection at relatively low currents.

It has been found extremely difcult to design automatic tripping systems that are totally dependent on a thermal element and are capable of providing protection at lower current values. More particularly, at low current values the I2 component which supplies the heat for deflection of the bimetal is so low that a bimetal of minimum cross section is necessary for directly heated thermal elements. As a result it becomes necessary to use a thermal element that is relatively weak mechanically and is not capable of providing suiiicient force for tripping. While this ditliculty may be overcome by utilizing indirectly heated bimetals, construction thereof presents additional manufacturing problems. The prior art has also sought to solve this problem by utilizing a magnetic tripping system which relies upon a movable magnetic member in a viscous fluid to change `a calibrating air gap. However, this last-noted design incorporates sealed components which are dicult and costly to manufacture.

In the circuit breaker of the instant invention, low current tripping is accomplished by utilizing both a bimetal and a magnet in combination. The bimetal needs to generate only a relatively small force to reduce the air gap in the magnetic system to a point Vwhere the flux lield of the magnet takes over and moves the armature with suicient r,torce to unlatch a circuit breaker contact operating mechamsm.

Accordingly, a primary object of the instant invention is to provide a novel relatively inexpensive circuit breaker automatic trip system for -operatingat relatively low currents.

Another object is to provide a novel trip system of this type, utilizing a directly heated thermal element.

Still another object is to provide a novel trip system of this type in which the thermal element and magnetic means cooperate to bring about automatic tripping at low current values.

A further object is to provide a novel trip system of this type in which deection of a bimetal element is effective to reduce the air gap in a magnetic trip means to a point where the magnetic trip means takes over and causes unlatching of the contact operating mechanism.

These objects as well as other objects of this invention 3,555,468 Patented Jan. 12, 1971 t. lCC

will become readily apparent after reading the following description of the accompanying drawings, in which:

lFIG. l is a side elevation of a circuit breaker, including the automatic trip mechanism of the instant invention, with the circuit breaker housing cover being removed to reveal the operating elements.

FIG. 2 is a plan view of the assembled magnetic and thermal trip elements, taken through line 2-2 of FIG. l and looking in the direction of arrows 2-2.

FIG. 3 is an exploded perspective of the elements shown in FIG. 2.

Now referring to the gures for a detailed description of the contact operating mechanism of circuit breaker 10, reference is made to my U.S. Pat. No. 2,996,589, issued Aug. 15, 1961, for a Pivoted Bimetal. Brieily, circuit breaker 10 includes molded housing 11, having internal formations for retaining the operating elements in their operative positions in a manner well known to the art. Operating mechanism 30, for bringing about the engagement and disengagement of cooperating contacts 22, 26, comprises cradle 31, which is pivoted at one end thereof at base protrusion 32. One end of main or operating spring 33 is tied to cradle 31 at a point intermediate the ends thereof, while the other end of spring 33 is tied to a midpoint of contact arm 27, having movable contact 26 at the lower end thereof. Operating spring 33 is always tensioned, thereby urging contact arm 27 upward into engagement with its pivot on the lower extension of manual operating member 28. Pivot 29 for member 28 is located just below a top opening in housing 1'1, thro-ugh which up- Ward extension 14 of member 28 extends to be manually engageable.

Parallel plate slotted arc extinguishing means 99 is operatively positioned to receive and extinguish electric current arcs drawn between contacts 22, 26 upon parting thereof. Contact arm kicker 66 is pivoted at 67 to cradle 31, with kicker end 68 being disposed within housing recess 69 for guided movement as cradle 31 moves to trip position, while the other end 65 of kicker 66 engages contact arm 27 with a sharp blow.

Latch tip 34 at the end of cradle remote from pivot 32 is engageable by latch 35 secured to control member 36 by welding. Pin 37 is also welded to member 36, with the ends of the former extending beyond the edges of member 36 and being received by pivot recesses in housing r11. Control member 36 is biased in a clockwise direction about pin 37 as a center by compression spring 40 disposed in a recess of housing 11, with one end of spring 40 abutting recess wall 42 and the other end of spring 40 abutting a portion of control member 36 above pivot 37. The normal or latching position of control member 36 is set by adjusting screw 43 which extends through an end opening in housing 11 and is received by nut 44 disposed in a suitable recess in housing 11. The free end of screw 43, opposite head 45 thereof, abuts control member 36 to bodily move the latter counterclockwise about pin 37 at the center.

Thermal-magnetic automatic stripping device includes a magnetic frame consisting of lower leg 71, upper leg 72, pin 73 connecting legs 71 and 72, and armature 74 pivotally mounted at its lower end to member 71. Coiled compression spring 76 mounted to pin 77 fbiases the upper end of armature 74 away from member 72 to normally form air gap 75 therebetween. Pin 77 extends through aperture 78 and armature 74 to the right thereof, with the enlarged head 79 on pin 77 normally abutting the left surface of armature 74. The right end of pin 77 extends through aperture 81 in the out-turned tab 82 at the upper end of spiral bimetallic element 80, with pin end I83 being turned at right angles to the main portion of pin 77 to mechanically secure pin 77 to bimetal 280.

Bimetal `80 is loosely Wound .on insulating bobbin 85 fitted over magnet pin 73 with ilange `86 at the lower end of bobbin 85 abutting the upper surface of lower magnet member 71. The lower end of bimetal 180 is maintained in relatively fixed position by being secured to the lower end 87 of conducting strap '88, whose upper end V89 is secured to the down-turned leg of load terminal 90.

Before explaining the automatic tripping operation of trip unit 100, it is noted that the current path through circuit breaker extends from load terminal 90 through strap 88, spiral bimetal 80, flexible braid 91, contact arm 27, movable contact 26, and stationary contact 22 secured to sta-b type line terminal 24.

The width of air gap 75 is adjusted by screw 93 entered into threaded aperture 94 in the down-turned leg of load terminal 90. Rotation of screw 93 acting through strap 8'8 bodily rotates spiral bimetal '80, thereby shifting the position of connecting pin 77 and the upper portion of armature 74 with respect to stationary pole face 95 formed by the left edge of magnetic frame member 72.

The width of air gap 75 may also be adjusted by rotating screw 103 threadedly entered into apparatus 104 extending through upturned leg 105 of magnetic frame leg 71. Head 106 is captured in housing recess 107. Thus, head 106 remains longitudinally fixed as screw 103 rotates and leg 105 moves left or right with respect to FIG. 1. This changes the position of the armature pivot to pivot armature 74 about link pin 77, thereby adjusting the width of magnet air gap 75.

While both adjusting screws 93 and 103 are shown, only one of them is required.

With circuit breaker 10 installed in an energized circuit, current flowing between line and load terminals 24, 90 flows directly through spiral bimetal 80, causing heating thereof. For additional heating of bimetal 80, strap l88 may be constructed of high resistance heater type material.

Since the lower end of bimetal `80 is essentially fixed, heating of bimetal 80 causes tab 82 to rotate in a clockwise direction with respect to FIG. 2. This moves connecting pin '77 to the right with respect to FIG. 2, therelby pivoting the upper end of armature 7'4 in a cloo wise direction with respect to FIG. 1, bringing it closer to stationary pole face 95, and in so doing reduces the air gap, thereby increasing the magnitude of magnetic flux in magnetic frame 71-7'4 and increasing the force available to overcome the force of biasing spring 76 and the friction forces between cradle latch tip 34 and latch 35.

When air gap 75 is suficiently reduced in thickness, the magnetic ilux generated by current flowing through the multi-turns of spiral bimetal '80 generates sufficient force attracting armature 74 so that the offset tip 97 thereof engages the lower end of member 36, pivoting the latter in a counterclockwise direction, thereby moving latch 35 to the right of latch tip 34 and releasing cradle 31. This tripping of operating mechanism 30 through the release of cradle 31 permits spring 33 to automatically separate movable Contact 26 from stationary contact 22 in a manner fully explained in my aforesaid U.S. Pat. No. 2,996,589.

Upon the occurrence of high fault currents, the magnitude of magnetic flux in frame 71-74 would be sucient to move armature 74 toward pole face 95, even lwithout repositioning of armature 74 through deilection of bimetal 80.

Thus, it is seen that the instant invention provides aV novel construction for a circuit breaker which, incorpo- 4 rating a directly heated bimetal, will trip at relatively low current values. The bimetal is very thin to achieve significant deflection at low current values. This is made possible by not requiring bimetal deflection forces to overcome contact latching forces.

Although there has been described a preferred embodiment of this novel invention, many variations and moditicaitons will now be apparent to those skilled in the art. Therefore, this invention is to tbe limited not by the specific disclosure herein but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined` as follows. f

1. A circuit breaker including a set of cooperating contacts, an operating mechanism for moving said contacts into and out of engagement; latch means for maintaining said mechanism in operating condition to permit said contacts to be engaged; biasing means; upon release of said latch means said biasing means urging said mechanism to a tripped position wherein said mechanism is incapable of operating said contacts into engagement; automatic trip means for releasing said latch means upon the occurrence of predetermined current overload conditions; said trip means including a magnetic trip means and a thermal trip means operatively positioned and constructed so that current ow in said circuit breaker generates magnetic flux for operating said magnetic trip means and generates heat for deforming a heatdeformable means of said thermal trip means; said magnetic trip means comprising a magnetic frame including a yoke and an armature mounted for relative movement; biasing means urging said yoke and said armature away from each other forming an air-gap therebetween which is normally of full width wherein said mechanism may operate said contacts into engagement; a mechanical connecting means joining said thermal trip means to said magnetic frame to reduce the width of said air-gap in relation to deformation of' said heat deformable means with the magnitude of said magnetic flux available to operate said trip means to release said latch means increasing as the width of said air-gap decreases; said connecting means constructed to permit movement of said armature toward said yoke without moving or deflecting said heat deformable means.

2. A circuit breaker as set forth in claim 1 in which the heat deformable means includes a bimetal element.

3. A circuit breaker as set forth in claim 2 in which the bimetal element is directly heated. i

I4. A circuit breaker as set forth in claim 2 in which the bimetal element constitutes an energizing turn for said magnetic trip means,

5. A circuit breaker as set forth in claim 4 in which the bimetal element is wound about a leg of said yoke.

4t. A circuit breaker as set forth in claim- 4 in which the mechanical connecting means extends between said armature and said bimetal element; said connecting means constructed to draw said armature closer to said yoke upon heating of said bimetal element.

7. A circuit breaker as set forth in claim 6 in which said armature engages said latch means for tripping of the latter when the thickness of the air-gap decreases below a perdetermined point.

8. A circuit breaker as set forth in claim 6 in which the mechanical connecting means provides lost motion permitting said armature to move toward said yoke Without deformation of said bimetal element.

9. A circuit breaker as set forth in claim 8 in which the bimetal element is a spiral wound about a leg of said yoke with one end of said spiral being relatively fixed and the other end thereof being relatively movable for operating the mechanical connecting means to move said armature in a gap closing direction.

10. A Circuit breaker as set forth in claim 9 in which the bimetal element is directly heated, said mechanical connecting means including a pin having a coil spring mounted thereon; said coil spring constituting the biasing means urging the armature and the yoke away from each other.

References Cited UNITED STATES PATENTS 6 3,244,835 4/ 1966 Locher 335--35 3,372,354 3/1968 Myers 335--176 3,417,360 12/1968 Eggers 337-368 5 HAROLD BROOME, Primary Examiner IU.S. C1. XJR. 337-90 

